An image display device in the form of a multi-projector system is known, wherein a plurality of images are projected from corresponding projectors, and synthesized and displayed on a screen. In such a multi-projector system, for example, it is necessary to ensure that seams between the projected images are made as less noticeable as possible.
Thus, the applicant has proposed an image display device wherein a calibration image is projected onto a screen, the projected image is captured by a capturing means, such as a digital camera or the like, and various calibrations are performed based on the captured data. An image display device of this type is disclosed, e.g., in Japanese Patent Application Laid-open Publication Nos. 2002-72359 and 2002-116500.
With a normal projector, a black level image is generated by an offset light, in which the signal levels are zero for the primary colors red (R), green (G) and blue (B). Such black level image is unstable in luminance within the image and tends to cause color shading of the image, so that calibration of the black level image (offset calibration) is necessary.
With the image display device disclosed in the above-mentioned Japanese Patent Application Laid-open Publication No. 2002-72359 or No. 2002-116500, however, the calibration image is captured without separation of the primary colors R, G and B. As such, it is difficult accurately to detect the color components of the black level image. Therefore, when a dark image is displayed, there tends to occur color shading of the image both within an image projected from a projector (intra-image shading), and between images projected from adjacent projectors (inter-image shading), thereby degrading the quality of the displayed image.
In order to correct color shading in the offset lights projected from the projectors, the applicant has already proposed a multi-projector system wherein a calibration camera is equipped with filters each corresponding to a primary color of the projector, so as to detect a luminance distribution of each primary color in the offset light, and to thereby acquire an offset correction data for correcting the color shading of the offset lights based on the luminance distribution. A multi-projector system of this type is disclosed, e.g., in Japanese Patent Application Laid-open Publication No. 2002-160475.
According to extensive experimental studies conducted by the applicant, it has been confirmed that the color shading of the projected images and the seams between the adjacent projectors can be mitigated. On the other hand, it has been also revealed that further improvement could be made with respect to the following points.
That is to say, with the above-mentioned multi-projector system, in order to detect the luminance distribution of each primary color of the offset light, the calibration camera is equipped with filters for the respective primary colors, which are narrow band range filters that do not allow transmission of the other primary colors. In this instance, not only the manufacture of the filters becomes difficult and the manufacturing cost of the filter increases, but also the light intensity upon capturing of the calibration image by the calibration camera becomes extremely low, requiring a prolonged exposure time for capturing the calibration image.
Moreover, when the projector is replaced and the spectrum characteristic of each primary color is thereby changed, the light of the primary colors projected from the current projector cannot be separated with the filters which had been effectively used for the previous projector, resulting in degradation in the correction accuracy of the color shading. As a countermeasure for such a problem, one may consider that the filter could be changed corresponding to the spectrum characteristic of the primary colors of the projector. To this end, however, a large number of filters with different band ranges must be prepared, thereby further increasing the manufacturing cost. Moreover, even if the filters are changed, there is no change in the basic situation where narrow band range filters are used, so that the problem of the prolonged exposure time for capturing the calibration image still remains unsolved.
The above-mentioned problems occur also when the color shading due to the offset light is to be corrected, in an image display device that is provided with a single projector, a CRT display, a liquid crystal display, or an LED display.
It is therefore an object of the present invention to provide a method for acquiring a correction data in an image display device, wherein the exposure time required for calibration can be shortened, and the change in spectrum characteristic of each primary color in the image display device can be effectively compensated so that the color shading of the image can be corrected highly precisely, without increase in the manufacturing cost.
It is another object of the present invention to provide a calibration system for such an image display device, wherein the method for acquiring a correction data can be carried out with a simple structural measure.